Field of the Invention
The present invention relates to an optical scanning apparatus and an image forming apparatus including the same and, more particularly, to the synchronous detection of a plurality of light fluxes in an optical scanning apparatus including a light source having a plurality of light-emitting points and a deflection unit such as a polygon mirror.
Description of the Related Art
There are currently demands for faster and smaller optical scanning apparatuses provided in image forming apparatuses such as laser beam printers and digital copying machines.
U.S. Pat. No. 6,476,955 discloses an optical scanning apparatus which includes a light source having a plurality of light-emitting points and can scan a scanned surface at once with a plurality of light fluxes (multibeam) in order to achieve high-speed scanning. This optical scanning apparatus causes a synchronous detection unit to electrically synchronously detect the positions of the dots formed by the respective light-emitting points, and electrically corrects write timings and image widths so as to accurately print an image.
In addition, U.S. Pat. No. 5,963,356 discloses a technique of integrating the optical element of an incidence optical system with the optical element of a synchronous detection unit, with light fluxes passing through the outside of a scanning optical system, in order to reduce the size of an optical scanning apparatus.
When, however, a multibeam is applied to the optical scanning apparatus disclosed in U.S. Pat. No. 5,963,356, since each optical element has a power within a main scanning section, the position of the dot formed by each light-emitting point is shifted by environmental fluctuations (for example, a temperature change). If the positional shift of each dot increases, the detection error in the synchronous detection unit increases, resulting in a failure in accurate printing.
According to the present invention, therefore, an optical scanning apparatus including a light source having a plurality of light-emitting points is required to reduce detection errors in the synchronous detection of a plurality of light fluxes which are caused by environmental fluctuations and to obtain a high resolution.